Method of making stem assembly for ultrahigh frequency electron tubes



June 2i, 1960 N. s. FREEDMAN METHOD OF MAKING STEM ASSEMBLY FOR ULTRAHIGH FREQUENCY ELECTRON TUBES Filed Jan. 2, 1952 2 Sheets-Sheet 1 INVENTOR NDRM I S. FREEDMHN TI'ORNEY June 21, 1960 N. s. FREEDMAN METHOD OF MAKING STEM ASSEMBLY FOR ULTRAHIGH FREQUENCY ELECTRON TUBES 2 Sheets-Sheet 2 Filed Jan. 2, 1952 INVENTQR NURMHN SFREEDMH United States Patent METHOD OF MAKHiG STEM ASSEMBLY FOR ULTRAHIGH FREQUENCY ELECTRON TUBES Norman Saul Freedman, Springfieid, Null, assignor to Radio Corporation of America, a corporation of Doinware Filed Jan. 2, B52, Scr. No. 264,551

3 (:iairns. (Ci.-29-155.55)

This invention relates to electron discharge devices suitable for ultrahigh frequency operation and concerns particularly the stem assemblies forming part of such devices, and to a method of making such'assemblies.

One type of electron discharge device employs a stem assembly comprising a flat glass disc or plate through which a plurality of lead-ins extend. The portions of the lead-ins extending from one face of the disc are usually relatively thick and constitute external contact prongs of the finished device in which the assembly is used. The portions of the lead-ins extending from the other face are usually relatively thin and serve as leads to electrodes within the device. These portions are usually made of nickel. The lead-ins also include an intermediate portion sealed to the glass disc. This portion may be of composite structure, for providing a good seal. One form of such composite structure is known under the commercial name of Dumet and includes a core of iron and a copper sheath clad on the core. The copper seals well to glass, and the composite structure as a whole has a radial expansion characteristic very closely matching that of'the glass for stability of the seal.

When the stern assembly referred to is used in an ultra high frequency electron discharge device, the leadins referred to are called upon to conduct ultra high frequency energy. As is Well known, such energy confines itself mostly to the surfaces of the conductors. Therefore, when the stem assemblies referred to are used in ultra high frequency devices, it is desirable that the surfaces of the lead-ins be characterized by good electrical conductivity.

One material having the desired high electrical conductivity is silver. Attempts have therefore been made heretofore to coat the lead-ins'of ultra high frequency electron tubes with silver. Such attempts, however, have not been fully successful.

One reason why such attempts have not been successful' is the fact that silver has a relatively low melting point. If the silver were applied as a coating to lead-ins prior to their incorporation in a stem assembly, it was reasonably assumed the coating would melt and flow away during the relatively high temperatures used in sealing the lead-ins through the glass disc of a stem. According to prior practices, therefore, the lead-ins were coated with silver after they had been scaled through the glass disc.

One practice foliowed has been to apply the coating to the lead-ins of a finished stem by electroplating. This has required that all the lead-ins he engagedby an electrode when immersed into an electroplating bath. One way in which this has been accomplished involved insertion of the lead-ins extending from one face of the disc into a socket having contact members engaging each lead-in and connected to an electrical source of desired polarity, and immersing the lead-ins extending from the other face of the disc into the 'electro-plating bath. This was "objectionable in that it required a double plating operation, since the portions of the lead-ins engaged by the socket were uncoated during the first operation and therefore a second plating operation for coating such portions was necessary. In addition to the fact that two platingoperations were called for, this practice was ob= jectionable because of the difficulty of threading the thinner lead-ins into the socket. This difiiculty arose because the thinner lead-ins are relatively long and usually have a diameter of. 20 mils. A further objection to this practice was the fact that the Dumet portion of the lead-ins and portions of the nickel leads adjacent the Dumet were sealed to the glass disc and therefore were inaccessible for coating. These uncoated portions constituted 'a break in the desired high conductivity paths along the lead-ins. In addition, where the thinner leads are formed to engage predetermined electrodes, they are incapable'of insertion in the plating'socket.

In view of the foregoing difficulties andobjections, the practice referred to was modified. According to the moditied procedure, all the thinner lead-ins extending from one face of the glass disc were brought together at their free ends and firmly engaged by an electrode in the form of a clamp. The entire stem assembly was then immersed into the electro-plating bath for coating with silver the leadin portions extending from both faces of the disc. Although this practice was an improvement in that it involved only one plating operation, it also was characterized by several objections. The inaccessible and sealed portions of the lead-ins, as indicated above, remained uncoated. The end portions of the lead-ins engaged by the clamp electrode were shielded from the electroplating bath and therefore were also uncoated. Furthermore, the clamping together of the'end portions of the lead-ins deformed them so as to require a subsequent time 'consurning operation of straightening out the deformities therein. Andhere again, when the thinner leadswere formed .as aforementioned, the coating procedure referred to could not be followed'since it was found impractical to clamp the thicker leads usually of 40 mils diameter.

Accordingly, it is an object of the invention to provide an improved method of making a stem assembly including coating with silver all'portions of the lead-ins thereof.

A further object is to provide a method of coating with silver all portions of the lead-ins of a stem assembly wherein the method involves a reduced number of operations. I 7

Another object is to provide an improved method of making a stem assembly wherein portions of the lead-ins are precoated with silver prior to incorporation in a'stem assembly and shielded from fires used in forming the assembly topreventloss of the precoated silver.

A further object is to provide a method of making a stem assembly havingilead-ins continuously coated with silver and involving precoating with silver portions of the lead-ins, sealing the lead-ins through a glass disc to form the assembly without harmfu'lly affecting the precoated portions, and subsequently coating with silver in one operation the uncoated portions of the lead-ins.

A further object is to provide a method of coating with silver all portions of thelea'd-ins of a stem assembly wherein a portion of the lead-ins are formed to engage desired electrodes.

Another object is'to provide a coating method for mating all portions of a group of lead-ins included in a stem assembly, wherein the method involves the steps of precoating portions of a plurality of said group of lead-ins in one operation, incorporating said groups of lead-ins in a plurality of stem assemblies, forming the uncoated portions to desired shape, and subsequently'coating' with silver the uncoated and formed portions of the lead-ins'in a single operation for each of said assemblies, whereby said lead-ins in each of said assembiles are coated-atall ice portions thereof in an operation including a portion of said precoating step and the entire of said subsequent coating step, and whereby the number of coating steps is reduced.

According to the invention, a stem assembly for an electron tube is provided in which the lead-ins thereof have a coating of silver on all surfaces thereof, including the surface of the intermediate Dumet portion thereof. Instead of being Dumet, this intermediate portion may be of iron. The stem assembly of the invention is therefore adapted to contribute to improved operation of an ultra high frequency electron tube in which it is used. The continuity of the silver coating along the entire length of the lead-ins provides a continuous high conductivity path from a source of ultra high frequency energy to which one end of the lead-ins is connected to electrodes within an electron tube, to which the other end of the lead-ins in connected.

The invention also provides an improved method of making a stern assembly having lead-ins, all portions of which are coated with silver. coating with silver the thicker portions of the lead-ins extending from one end thereof to at least a portion of the thinner leads adjacent the other end and spaced from the Dumet. This coats the portion of the lead-in included in a seal and the portion extending from one face of the glass disc in a stem assembly.

The precoating may be accomplished in one of two ways. The precoating may be applied to a continuous stock of Dumet wire and to continuous stocks of nickel wire of the required diameters to serve as the lead-in portions extending from said ends of the Dumet portion. The continuous stocks referred to may then be cut to suitable lengths and butt welded in end-to-end relation. This fixes one end of the silver Dumet wire to predetermined lengths of silver coated nickel lead-in wire to provide a lead-in having a continuous silver coating.

The precoating may be alternately effected after the lead-in portions comprising the Dumet wire and the two lead-in portions have been welded together as indicated above, to form a lead-in. According to this alternative step, a-plurality of lead-in assemblies, say at least twice .as many as are required for a stern, are simultaneously subjected to a coating step in which a portion only of the lead-ins are coated. This portion extends from one end of the lead-ins and includes the Dumet, the thicker portions and a portion of the thinner lead-ins extending from the Dumet.

After the precoating step is completed by either of the foregoing steps, the lead-ins are sealed through a glass disc. The sealing step involves supporting the lead-ins in a mold in a suitable array, fusing a glass cullet or short tube disposed around the array referred to, by directing fires thereto, and forming the fused glass to desired disc shape through which the lead-ins become sealed, with the Dumet portion of the lead-ins and portions of the thick and thin leads included in the seal. The mold usually includes a lower mold having a plurality of wells for receiving the thicker portions of the lead-ins, the wells having a depth for disposing the Dumet portion and a portion of the thinner leads between the ends of the cullet referred to. Therefore, by placing the thicker and precoated ends of the lead-ins into the wells referred to, the lower mold and the cullet effectively shield the precoated portions from the sealing fires and thus prevent loss of the silver coating which would otherwise occur by melting and flowing away. When theentire lead-in assembly was precoated with silver, it is likely the portion thereof exposed to the sealing fires may lose its silver coating. Stem assemblies formed with such leadins are therefore further processed in thesame manner as assemblies having partly coated leads, as beforementioned.

The product of the foregoing steps is a stem assembly having lead-ins, a portion ofwhich is coated with silver.

The method involves pre-' The only portion of the lead-ins that remains uncoated is the portion extending from one face only of the stem disc. This uncoated portion may not be formed, as indicated above. The final step of the method of the invention involves coating such uncoated and formed portion with silver. This final step is accomplished by inserting the relatively thick and coated lead-in portions extending from the other face of the disc in a socket and immersing the exposed uncoated portions of the lead-ins in a silver plating bath.

Form the foregoing, it will be appreciated that the method of the invention is more economical in the steps required, than the prior practice of first coating the lead ins extending from one face of a stem disc, and their coating the lead-ins extending from the other face thereof. In the method of the invention, one precoating step only is necessary for accommodating a plurality of final coating steps. Furthermore, the method of the invention results in'the application of a continuous silver coating to the lead-ins including the Dumet portion of the lead-ins, which was impossibleunder the prior practices referred to. In addition, no clamp is required by the method of the invention, and therefore the disadvantages of absence of coating at the clamped region of the leadins and the need to straighten out the clamped leads, are avoided. Also, formed leads may be coated by the meth od of the invention. This permits forming the leads prior to the coating application. When the silver coating is applied before the leads are formed, the subsequent forming operation may strip the silver coating, thus requiring are-coatingstep. This'aspect of themethod of the invention therefore results in a cost saving, not only in operator time but in the amount of silver required.

While the invention is pointed out with particularity in the appended claims, it may best be understood by reference to the following detailed description of embodiments thereof, takenin connection with the appended drawing in which:

Figure l is an elevational view partly in section of an ultrahigh frequency electron tube incorporating the stern assembly of the invention;

,Fig. 2 shows an elevation partly in section of a stem assembly having lead-ins coated with silver in accordance with the invention;

Figure 3 shows an elevation partly in secion of molds and sealing'means used in forming a stem of the type shown in Figure 2;. v

' Figure 4 is an elevation partly in section of apparatus used in a, prior method of coating stem lead-ins with silver;

7 Figures 5, 6 and 7 show apparatus useful according to one form of the method of the invention in precoating portions of a lead-in prior to inclusion in a stern assembly; Figure 5 being .a view in elevation and partly in cross-section of an apparatus for silver coating a continuous stock of such portions; Figure 6 being a sectional elevation of a cutting apparatus for cutting the coated stock to desired length; and Figure 7 being a side view of coated portions of a lead-in in end butt relation for welding and showing a preferred arrangement of welding electrodes;

Figures 8 and 9 depict apparatus that may be used in another form of the method of the invention in precoating with silver portions of a lead-in prior to inclusion in a stem assembly; Figure 8 being a side view of uncoated lead-in portions in end butt relation and showing an arrangement of welding electrodes that may be used; Fig ure 9 being an elevation partly in section of an apparatus for precoating a selected portion of the lead-ins;

Figure 10 is an elevation, partly in section, of apparatus that may be used in coating the portions of the leadins left uncoated by the precoating step;

Figure 11 is a fragmentary sectional view of a portion of the stem assembly of the invention and shows a lead-in, including the several portions thereof, extending through the glass disc of the assembly;

Figures 12, 13 and 14 are views in cross-section of longitudinally spaced portions of the lead-inshown in Figure 11; Figure 12 showing a cross-section of the Dumet portion of the lead-in and depicting the silver coating thereon, Figure 13 being a cross-section of the wire welded to one end of the Dumet and having a silver coating thereon, and Figure 14 being a cross-section of the wire welded to the other end of the Dumet and showing the silver coating thereon; and

Figure 15 is an elevation partly in cross-section and shows a stem assembly having formed leads coated in accordance with the method of the invention.

Referring now to the drawing in more detail, Figure 1 shows an ultra high frequency electron tube having an envelope 20, closed at one end by a glass disc '21 forming part of a stem assembly. In addition to glass disc 21, the stern assembly includes a plurality of lead-ins 22 connected to electrodes of electrode assembly 23. The portions 24 of the lead-ins 22 are relatively thick, and may have a diameter of 40 mils and are adapted to be inserted in a socket, not shown, for connecting the electrode assembly to suitable sources of ultra high frequency electrical energy, not shown.

According to the invention, all portions of the lead-ins 22 are coated with silver. As shown in Figures 2, ll, 12, 13 and 14, these portions include the relatively thick wire 24 extending outside of the envelope 2%, a relatively thin wire 25 which may have a diameter of mils, extending within the envelope and suitably formed as shown in Figure 15 for connection to an electrode of electrode assembly 23, and a wire 26 intermediate Wires 24, and end welded thereto, to thereby constitute a continuous lead-in. The Wires 24, 25 may be made of nickel. The intermediate portion 26 preferably is a composite structure, including a core 27 of iron, and a sheath of copper 28 (Figure 12). Such composite structure is known by the trade name of Dumet and may have a diameter of 16 mils. Each of the wires 24, 25 and the Dumet 26 in a stem assembly according to the invention, has a coating of silver 29 thereon as shown in Figures 11 to 14. The coating of silver is continuous from the free end of wire 24 to the free end of wire 25, to therebyprovide a continuous path of high conductivity for ultra high frequency energy from a socket, not shown, to the electrode assembly 23.

Heretofore, stern assemblies have been provided in which the wires 24, 25 thereof have been partly coated with silver. No prior stem assembly is known in which the Dumet portion 26 is also so coated as well as pertions of wires 24, 25 included in the seal through the glass disc 21. The reason for failure heretofore to coat with silver the portions of the lead-in passing through the glass disc 21, is believed to reside in a conclusion that applicant has found to be erroneous, to the etfect that any silver applied to the Dumet prior to sealing the lead-ins to the disc, would melt and flow away as a consequence of the relatively high sealing temperature used. This result was also believed to be characteristic of any silver coating applied to the wires '24, 25 prior to the sealing operation. In consequence of this conclusion, therefore, prior practices involved sealing uncoated leadins to a glass disc, the portions of the lead-ins extending from the two faces of the disc being subsequently coated either in two separate operations or in one operation as aforementioned.

When two operations were employed, the prior practice involved inserting the lead-ins extending from one face of the disc into a socket for support and desired electrical connection to a source of negative polarity, and immersing the lead-ins extending from the other face of the disc into a silver plating bath for coating the last-named leadins with silver. The stem assembly was then removed from the socket and the coated lead-ins inserted therein for a repetition of the process for coating the remaining. uncoated lead-ins. The Dumet, and portions 'of the nickel leads sealed to the glass of the disc were shielded from the'silver'bath in both operations, with the result that the Dumet and such portions wereuncoated.

Where one operation was employed heretofore for coating the lead-in portions extending from the opposite faces of the'glass disc of the stemassembly, the lead-ins extending from one of said faces were clamped at their free end to electrically connect all the lead-ins to a source of negative polarity, as shown in Figure'4. The entire assembly was then immersed into a silver plating bath. While this *economized in the number of operations required, it was characterized by several disadvantages in addition to that of leaving uncoated the Dumet and the other portions of the lead-in sealed in the glass disc. Among these disadvantages was the fact that the clamp 30 shielded-the portion of the lead-ins engagedthereby from the silver bath as a consequence of which this portion failed to receive a silver coating. This uncoated portion contributed a further break, in addition to that of the uncoated portions referred to, in thedesired high conductivity path. Afurther disadvantage resided in the fact that the deformation in the lead-ins resulting from the clamped engagement thereof, requiredcorrection before the stem was incorporated in an electron tube. The correction referred to involved straightening the bent lead-ins, which was 'a'tedious manual operation. Moreover, this coating practice was not feasible when the leads were formed prior to coating. It will be noted therefore, that prior art methods fo coating lead-ins with silver were incapable of coating with silver the Dumet portion and other portions thereof involvedin the seal, and without resorting to two full op erations, were even incapable of fully'coating the exposed portions of the lead-ins.

According to the method of the invention, steps are provided for silver coating all portions of the lead-ins referred to. Following one form of the method, continuous stocks of wire of the desired diameters and continuous stock of -Dumet wire are silver coated in similar ways. The apparatus used in one example is shown in Figure 5. A continuous stock 31 which may be either Dumet or nickel wire as aforementioned, is fed by reel 32 and idler 34 through a silver bath 35 contained in receptacle 36 and collected in coated form'b-y reel 33. A silver rod 37 connected to a source of positive polarity (not shown) extendsinto the bath referred to. A contact member 38 connected to a source of negative polarity (not shown) contacts the wire 31.

After the wire stock 31 has been coated with silver in the foregoing manner, the coated stock is cut into desired lengths 39 by the apparatus shown in Figure 6. The apparatus includes a support 40- along which the coated stock is fed until it abuts against stop 41. The support is provided with a recess 43 spaced from stop 41, a distance equal to the desired length of the lead-in portion 39. A movable knife 42 is mounted for movement in a path in registry with recess 43 for severing the stock at the portion thereof traversing said recess. If desired, stop 41 may be adjustable to permit cutting coated Dumet wire as well as coated nickel wire, which are usually of diiferent lengths. As an alternative, a separate apparatus may be provided for cutting each of the coated Dumet and nickel wire stocks to required lengths.

The next step involves end welding the cut and coated Dumet wire 26 (Figure 7) to coated lengths of nickel wire 24, and'25. In order to avoid displacement of the silver coating at the regions of the welds, two sets of welding electrodes 44, 45 and 46, 47 are preferred, the electrodes in each set being relatively closely spaced, and with electrodes 45, 46 connected to a negative potential source to avoid current flow through the coated-Dumet 26. While the welding temperature is higher than the melting point of silver, the welding operation is preferably controlled in the manner described in copending application of Parker and Garner, Serial No. 17,824, filed Mar. 30, 1948 and assigned to thesame assignee as the present application and now' Patent No. 2,625,637. According to the arrangement there described a sufficiently high power is employed so that the time required for a weld may be so short that no material flow of metal has time to occur.

The fact that the elements are coated with silver prior to the welding step is advantageous in that the welds formed may be in the nature of brazes and thus require fusion of the silver only, at the regions of the weld. This permits reduced temperatures to be used, thus reducing the danger of coating loss at regions spaced from the welds.

A desired number of lead-in assemblies made as indicated in Figures 5, 6 and 7, are then sealed through a stern to provide the stem assembly shown in Figure 11. The apparatus that may be used in the sealing operation is shown in Figure 3. The apparatus includes a lower mold 48 having a plurality of wells 49 therein for receiving the thicker portions 24 of the lead-ins 22. In the example shown seven lead-ins are used and accordingly seven wells are provided in the mold 48. The wells terminate in bottoms 50 which serve as stops to limit the downward extent of the lead-ins in the mold, so that the welds 51 of the lead-ins are disposed adjacent the upper surface 52 of the mold. The wells referred to may be disposed in a circular array. Around the circular array of lead-ins positioned in well 49 is placed a short length of glass tubing or cullet 53 which restson surface 52 of the mold. V The cullet 53 extends upwardly and parallel with the lead-ins 22, a distance greater than the length of the Dumet portion 26 of the lead-ins. Nozzles 54, 55 serve to play fires on the cullet 53 to soften it to plastic state. To distribute the heat from the fires evenly aroundthe cullet, the lower mold 48 may be caused to rotate axially, by means not shown. To shield the upper or thinner parts 25 of the lead-ins an upper mold 57 having wells 58 may be lowered against the upper edge of cullet 53.

Applicant has found the lead-in portions 24, Dumet portions 26 and leads 25 are effectively shielded in the arrangement shown from the fires from nozzles 54, 55 so that their temperature is not raised to the melting point temperature of silver and consequently no loss of silver coating occurs. Thus the presilvered portions 24 are shielded by being disposed in the wells 49, the presilvered Dumet portions 26 are shielded by the cullet 53 and the presilvered portions 25 are shielded by mold 57.

After the cullet has been made sufiiciently plastic, as indicated above, the upper mold 57is caused to move downwardly to press the plastic cullet to the disc form 21 shown in Figure 2. The upper mold is caused to rotate by means, not shown, in a manner similar to lower mold 48, with the wells 49 therein in registry with the wells 58 in the upper mold. The lower ends 58a of wells 58 are flared, as shown in Fig. 1, to form the bosses 21a around ends of the leads 25 as depicted in Figs. 2, l1 and 15.

An alternate procedure is permissible in sealing the silver coated leads 22 through the glass disc 21. According to this procedure, the upper mold 57 is inraised position as shown in Figure 3. In the arrangement shown, it will be noted that the cullet 53 extends appreciably above the upper ends of Dumet portions 26. Therefore, as the cullet is softened by the fires from nozzles 54, 55 and partly collapses, applicant has found that the collapse does not reduce the length of the cullet tosuch extent that its shielding function with respect to Dumet 26 and a portion of lead 25 adjacent the Dumet is lost. It has been found by applicant that after such collapse occurs, the cullet extends upwardly at least as high as to shield the portion X of the lead 25 from the sealing fires. This portion of the lead 25 extends from the weld 56 to the top of boss 21a after the stem is formed, as shown in Fig. 11. The alternate procedure described thereforealso assures a'coating of silver on the portions of the lead-in involved 'in the seal. One advantage of the alternate procedure lead-in is precoated with silver and portion 25 is unshielded from the fire, it is likely that any silver remaining on the upper unshielded portion of this lead will be depleted or entirely lost by stripping during the lead forming step. Such loss of silver may be tolerated in view of the saving the practice permits in apparatus modification, as aforementioned.

When the sealing step is carried out in such manner that the entire lead-in is shielded from the sealing fires, the lead forming operation may cause loss of silver coating on the formed leads 25 shown in Figure 15. Therefore, when either sealing procedure described is followed, it is desirable to coat the portions of the lead-ins 25 extending from the disc 21 in a subsequent step.

The stem assembly, shown in Figure 15, formed by the foregoing forming and sealing operations is accordingly then inserted in a socket 59 shown in Figure 10, with the coated portions 24 received in openings 60 of the socket. The socket has contact members 61 connected to an electrical source, not shown, of negative polarity. The socket is then extended into silver plating bath 62 in container 63. A silver rod 64, connected to an electrical source (not shown) of positive polarity is extended into the plates both to provide a source of plating material. This step serves to coat with silver the previously uncoated portions 25 of the lead-ins.

It will be noted that by the foregoing method, all portions of the lead-ins 22, including the sealed portions thereof, are coated with silver, and that the silver coating remains in place during the fabrication of the stem assembly, so that in the completed stern assembly, lead-ins of high conductivity at ultra high frequency are provided. The silver coating on each of the lead-ins is characterized by continuity from one end of the lead-in to the other. The absence of such continuity, which characterized prior lead-in assemblies, is avoided, for improved operation of an electron tube in which the assembly is used.

The operation of precoating the lead-ins with silver may be carried out according to a different form of the method of the invention. Thus, instead of precoating the lead-ins by coating continuous stock of such portions thereof as shown in Figure 5, the lead-ins may be made of uncoated parts welded together as shown in Figure 8. The parts referred to comprise uncoated nickel wires 24, 25 and uncoated Dumet wire 26 of predetermined lengths to provide a lead-in assembly of desired length. Welding electrodes 65, 66 may be mounted to engage the portions 24', 25 for making desired welds between the Dumet 2 6 and the wires 24, 25, no problem of coating loss due to the welding temperature being involved in this example.

After the wires referred to are welded together, a plurality of the resultant lead-in wires, say twice as many as are required for a stem assembly, are mounted on holder 67 shown in Figure 9, which is connected to an electrical source, not shown, of negative polarity. Holder 67 has openings 63 for receiving portion 25 of the leadins and includes contacts 69 for connecting the lead-ins to the electrical source mentioned. The holder 67 is positioned so that the portions 26 and 24 of the lead-ins depend therefrom and may be lowered into container 79 having plating bath 71 until the welds 56 and portion X of leads 25 become immersed in the bath. Stops 67a are provided for determining the aforementioned degree of immersion. The usual silver rod 72 connected to a 9 source of electrical energy of positive polarity, extends into the bath to provide the necessary coating material.

After the lead-ins have been coated with silver in the .foregoing manner, a predetermined nulmber thereof, say seven, are sealed through a glass disc, as explained above in connection with the forming and sealing step illustrated in Figure 3. In this case no precaution need be taken to shield the upper uncoated portions of leads 25. Thereafter, the remaining uncoated portions of the lead-ins are coated as previously explained and illustrated in Figure 10.

While the precoating operation may be carried out either according to the steps of Figures 5, 6 and 7, or the steps of Figures 8 and 9, the steps illustrated in Figures 8 and 9 are preferred because a saving in silver results and changes in existing sealing apparatus are avoided.

As indicated before herein the intermediate portion of a lead-in assembly may be made of iron only and coated in accordance with the method of the invention. This results in economy, since the sheath of copper is omitted.

It will be appreciated from the foregoing that a novel and advantageous method is shown for making the stem assembly referred to.

What is claimed is:

1. Method of making a stem assembly including a glass disc and lead-ins extending through said disc, the portion of each of the lead-ins extending from one face of said disc being formed for facilitating connection to electrodes, and wherein said lead-ins have a continuous coating of silver thereon from one end to the other, said method comprising the steps of coating with silver a portion of each of said lead-ins extending from one end thereof, shielding said portion with a cylindrical mold and a tubular glass work piece disposed in end to end relation and surrounding said portion, heating said glass work piece to partial collapse while substantially preserving its shielding function, pressing said heated glass work piece to disc form and in sealing engagement with said portion to form said stem assembly, with an uncoated portion of each of said lead-ins extending from one face of the glass disc, forming said uncoated portion of the lead-ins to predetermined bent shape to dispose said lead-ins in proximity to predetermined electrodes, and subsequently coating with silver said uncoated portion of each of said lead-ins, whereby said lead-ins provide high conductivity paths for ultra high frequency energy to said electrodes.

2. Method of coating with silver lead-ins extending through a stem, comprising first coating with silver an intermediate portion of each of the lead-ins to be included in a glass-to-metal seal through said stem and an end portion of each of the lead-ins extending from said intermediate portion to one end of each of the lead-ins, supporting said lead-ins with said end portion and intermediate portion of each of the lead-ins extending into wells in a mold and into a fusible tubularglass work piece supported on the mold, respectively,

directing heat to the outside surface only of said glass Work piece to render the glass thereof plastic, whereby said intermediate portion and said end portion of each of said lead-ins are shielded from heat, pressing the plastic work piece to form it around and into engagement with the silver coating on the intermediate portion of each of the lead-ins, whereby the silver coating on said intermediate and end portions of each of said lead-ins is preserved from loss and a stem assembly is provided having lead-ins coated at the locations of the seals of the lead-ins therethrough and at the portion of each of said lead-ins extending from said one face of the stem, :and subsequently silver coating the remaining uncoated portion of each of said lead-ins, whereby said lead-ins are characterized by relatively high conductivity at ultra high frequencies.

3. Method of making a stem assembly for an electron discharge device, comprising the steps of coating with silver three continuous stocks of difierent diameters to provide a continuous silver coating throughout the entire lengths of said stocks, cutting said stocks to predetermined lengths, placing in end but-t relation three of said lengths comprising wire from each of said stocks, heating said three lengths while in end butt relation to fuse a portion only of the silver coating adjacent to the abutting ends of said lengths for fixing said lengths in said relation to form a lead-in having a continuous coating thereon from one end thereof to the other, supporting one end portion of said lead-in in a mold and disposing an intermediate portion of the lead-in within a tubular glass work piece positioned on the mold, directing a heat source to the outer surface only of said work piece to render said work piece plastic, whereby said end and intermediate portions of said lead-in are shielded from said heat source, and pressing said plastic glass work piece against a surface of said mold to flat shape and in sealing engagement with said intermediate portion of said lead-in, whereby said lead-in has a coating of silver on at least said one end portion and on said intermediate portion thereof.

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